Prior art hybrid powertrains typically include an internal combustion engine, an electric motor, and a transmission. The crankshaft of the engine, the rotor of the motor, and the input shaft of the engine are selectively interconnected by various torque-transmitting mechanisms. These torque-transmitting mechanisms have been necessary in the prior art to disengage the engine from the motor and to disengage the engine and the motor from the transmission.
More specifically, in a typical prior art hybrid powertrain, the crankshaft of the engine is selectively connected to the rotor of the motor by a clutch. When the clutch is engaged, the crankshaft and rotor rotate in unison; when the clutch is disengaged, the engine is disconnected from the rotor and the transmission. In one mode of powertrain operation, the clutch is engaged, and the engine, either by itself or in combination with the motor, supplies motive power to the drive wheels via the transmission. In another mode of powertrain operation, the motor supplies all motive power to the drive wheels, and the clutch is disengaged in order to prevent the motor from turning the crankshaft and attendant pumping losses as air is drawn through the intake manifold, engine cylinders, and exhaust manifold. Similarly, during regenerative braking, the clutch must be disengaged to prevent crankshaft rotation and attendant pumping losses.
The rotor of the motor is connected to the transmission via a hydrodynamic fluid drive such as a torque converter. The torque converter provides a fluid coupling between the motor rotor and the transmission input shaft upon sufficient rotor torque and speed.
Many vehicle accessories, such as power steering pumps and HVAC compressors, are connected to the crankshaft by belts, chain drives, etc., to be driven by the engine. Thus, the engine must be on and consuming fuel to drive the accessories, even when only the motor is propelling the vehicle or when the vehicle is at rest.